Conventionally, a valve device for an exhaust gas recirculation (EGR) unit is known to have a cantilever bearing structure. JP-A-2007-285311 (US 2007/0240690) describes such a valve device in which a rotating shaft and a valve are rotatably supported from only one side of a passage.
In such a valve device, a bearing member supporting the rotating shaft is placed on one axial side of the rotating shaft, and has a metallic bearing and a ball bearing. The metallic bearing is placed to be closer to the passage than a ball bearing is. The metallic bearing is press-fitted and supported in a bearing hole of a housing, and a clearance is defined between the metallic bearing and the rotating shaft in a radial direction. And the ball bearing is supported between an inner race press-fitted into the rotating shaft and an outer race press-fitted into the bearing hole.
Thus, the metallic bearing having a high heat resistance and the like is placed to be closer to the passage, and the ball bearing, which is a generic bearing, is placed to be further from the passage. Furthermore, with consideration for the clearance between the metallic bearing and the rotating shaft in the radial direction, the metallic bearing and the ball bearing are located away from each other in an axial direction to restrict axial runout. And an oil seal is placed between the metallic bearing and the ball bearing to keep fluid-tightness.
However, while needs for reducing a producing cost of a valve device are getting increased, the cantilever bearing structure is also required to be simplified to reduce the producing cost.